Improvement in twist-drills



To all whom it mag/concern: v

" `-socEArEsl seHoLEIELD, `or PROVIDENCE, RHODE Letters Patent No. 97,818, dated December 14, 1869.

IMPRUVEMENT IN' TWIST-DRILLS.

The Schedule referred to in thune Letters Patent and making part of the same'.

Be it known that I, SOCRATES ScHoL'FiELD, of Providence, in the county of Providence, and State of Rhode Island, havelinvented an Improvement in Drills;

and do hereby declare that the following is a full and exact description, reference being had to the accom-A panying drawings, making a part of this specification. The nature of my invention consists in the use of certain guiding-lines or grooves upon twist or other similar. drills, as a permanent guide to the workman, whereby they may be ground properly.

To enable those skilled in the art to make ,and use my invention, I will proceed to describe its construction and operation.

Figure 1 represents a side view, and Figure `2, anend View, showing the position of the lines contemplated.

that it may always drill-a hole of the same size.

"orderthat ythis end may be secured, I tracel the lines v.a a and a a', lougitudinallygat the bottom of each In the matter of grinding a commontwist-drill, it is very essential that the properceutre be preserved, so In groove, which lines are to-constitute a Working-gauge for `the length of each cutting-lip, and should be drawn on opposite sides, a little out oftheceutre of the drill,

so that the centre penetrating-edge a a may run di- `agonally from thebottom of onegroove to *the other,

as shown in fig. 2. p

It will be readily perceived thatpit' the lines a a, and a a', were-drawn lin the exact centre, and opposite l each other, the proper angle for grinding eachtlip of the drill could not well be preserved, since af diagonal edge, a a', is the result of the intersection'of the two inclined surfaces of the end ofthe drill, when properly ground.

p On the outer surfaceof thedrill maybe traced the parallel lines l1 b and bb, in order to furnish a gauge whereby the proper angle of the` cutting-edge may be preserved, sincethe distance to the nearest line b and b may-be easily estimated by the eye, and made the same in both.` .i

Thus, by starting at the diagonal centre-line a a', and reaching apoint on each lip at the same distance from its nearest outside line, the proper centre and anglemay be easily determined by inspection.

The lines b b and b b', may be traced about a quarter of an inch apart upon the surface of the drill,

-gow...

either. directly around the drill, orA in the form of a double screw-thread,v which will also give corresponding lines on oppositefsides of the drill.

Themodeof putting on the lines a a and a a', may be varied. I prefer the use of a diamond in 'making a scratch or groove, to indicate the proper lines, the point of the diamond` being pressed to the groove of' the drill by a spring or weight, so as to produce a uniform cut throughout, as the drill is being` turned and drawn backward. j

This cent-re line or groove may be made of anyde-` sired width, one edge being taken, when very Wide, as the proper location. of the inner corner of the cuttinglips. l

These lines mav also be etched by means of anacid bath, after being traced on a waxed surface by suitable mechanism, or they may be merely stainedupon the surface of the steel by the use of proper chemicals,

' the necessary requirement being permanence, and that they should present on the 4side toward the cutting-lip a smooth and well-defined edge.

l am aware, that in the extensive manufacture of twist-drills, as a specialty, acertain milling-tool has been used for rough-ing out, which leaves a faint sort of line in its track at the centre of the drill, but such line has been produced without reference to the proper position ofthe inner corner of the lip, and hasinvariably been either obliterated by another cutter, or filed out, ,so4 as not to` appear on the finished drill; therefore I do not claim such accidental line, made during the primary stage of the drills manufacture, when, asV heretofore, not retained as of use iu the finished drill, for the` purpose specified; but

What I claim as my invention, and desire to secure by Letters Patent, is

` Aitwist, or other similar drill, marked with distinctl centre-guiding lilies' or grooves a a and a a', for the purpose of indicating the properposition ofthe inner corner of each lip in glinding.` Also, the combination of the parallel exterior' lines `b l) and b' b', with the centre-guiding lines an. and a.'

d', substantially as described.

SOCRATES, SGHOLFIELD. l

-Witnesses:

A. G. SCHOLFIELD, A. It. ABEorr. 

